I "think" they might make them in normal vehicle sizes. I would only consider it a good solution in two situations ... long periods with no charging, or hard to start engine. As krisr mentioned ... they spin over an engine like you wouldn't believe.
I was paying $200 each for quality Yuasa batteries for my Honda RC51 every two years, and even fully charged you would have about three attempts to start the engine and they were done. With this LiFEPO4 battery you could put it in gear, hit the starter button and drive on the starter if you wanted to
So in my case the $250 was worth it.
Lke krisr mentioned, it has onboard battery management that protects it pretty well.
After looking at the brand I bought (EarthX) it appears the largest is like 6x6x6, about 13 pounds, 800 CCA something like 1600 PCA. So yes, quite small. Prices I was quoting look like they were for their aircraft batteries ... so maybe $500.
They don't have nearly the voltage drop during starting that a lead acid battery does, which is why they turn the engine over so nicely.
Losing 40 lbs in the front corner of the car would be nice
PS: Here is a random brand I found on Amazon:
https://www.amazon.com/Powertex-Batt...47c48c32f&th=1